The invention relates to a device for separating metal deposit from a mother plate used as a cathode in the electrolytic process, as metal electrorefining or metal electrowinning.
The refining of many metals, such as copper, zinc and nickel, includes electrolytic process where harmful impurities are separated from the metal to be produced. The metal produced in the electrolytic process is gathered on the cathode by means of electric current. Usually the electrolytic process is carried out in tanks filled with an electrolyte containing sulphuric acid and, immersed therein, a number of plate-like anodes and cathodes made of some electro conductive material and placed in an alternating fashion. At the top edges, the anodes and cathodes are provided with lugs or bars for suspending them at the tank edges and for connecting them to the power circuit. The metal to be produced is brought into the electrolytic process either as soluble anodes in electrorefining process, or as dissolved in the electrolyte at some preceding process stage, in which case the employed anodes are insoluble in electrowinning process.
The cathode used in the electrolytic process can be produced of the desired metal to be produced, in which case the deposit need not be stripped from the original cathode plate. Usually, however, the cathode, i.e. the mother plate, to be immersed in the electrolytic tank is made of some other metal than the one to be produced. Such materials of the mother plate can be for instance stainless steel, aluminium or titanium. In that case the metal to be produced is gathered on the surface of the mother plate in deposits, which are removed from the mother plate at defined intervals.
Owing to electric current, the metal produced in the electrolytic process is accumulated in deposits on all electro conductive surfaces of the mother plate, i.e. if the mother plate is completely electro conductive, the metal to be produced covers in a uniform deposit the mother plate in all parts immersed in the electrolyte. In order to facilitate the removal of the deposits of the metal to be produced from the surfaces of the mother plate, it is necessary to affect the metal to be produced from accumulating deposits over the narrow edges of the mother plate, i.e. the edges of the mother plate must be made non-conductive.
The best-known way to make the edges of the mother plate non-conductive is to cover the edges with edge strips made of some insulating material, such as plastic. Generally the insulating strips are plastic profiles with a groove-shaped cross-section and are pressed onto the edges of the mother plate and remain in place either owing to the pressure created by the transformation, by rivets inserted through the mother plate or due to a combination of these. When the deposits are removed from the mother plate by stripping, it is possible that the edge strip positioned on the edge opposite to the edge where the hanger bar is installed will be damaged if there is no protection over the strip. Therefore, instead of a plastic edge strip on the edge opposite to the edge where the hanger bar is installed wax is used as a non-conductive material in order to produce two separate deposits, or the deposits are allowed to grow uniformly around the bottom of the mother plate producing a single deposit. The problem with wax is that it has to be washed off from the mother plate and from the deposits prior to the separation of the deposits and then re-applied on the mother plate after the separation, and that some wax may still be in the deposits after washing causing some contamination of the produced metal. The problem with the single deposit is that it is much more complicated to handle the deposit during the separation of the deposit from the mother plate and that the single deposit is not well suited for some end use applications.
The object of the present invention is to eliminate some of the drawbacks of the prior art and to achieve a new and viable device for separating the metal deposits created in the electrolytic process from the mother plate by affecting at least partly the growth of the deposit on the edge or on the vicinity of the edge of the mother plate opposite to the edge where the hanger bar is installed. The essential novel features of the invention are apparent from the appended claims.
According to the invention the cathode to be treated in the device of the invention contains a plate-like mother plate and a hanger bar which is installed on one edge of the mother plate. The mother plate of the cathode is provided on the edge or on the vicinity of the edge opposite to the edge where the hanger bar is installed with a means for preventing partly the growth of the metal deposit. The growth affecting means is advantageously for instance a groove in the edge or in the vicinity of the edge of the mother plate or the mother plate is made longer than the respective anode in the metal electrorefining or metal electrowinning process and the precipitation speed in that additional area is decreased and the growth of the metal deposit is then slower. By using the area where the growth of the metal deposit is at least partly affected, the metal deposit is divided into two separate pieces during or after the removing process of the metal deposit.
The growth affecting means of the invention at least partly prevents an essentially uniform growth of a metal deposit on the surface of the mother plate in order that when the metal deposit is bent, the metal deposit is broken in two parts on the location of the growth affecting means. In one embodiment the change in the growth of the metal deposit is based on that the groove to be used as the growth affecting means is shaped so that the grain structure in the metal deposit is changed and the bending properties on that part of the metal deposit are changed. The growth affecting means is for instance a wedge-shaped groove which walls are in an acute angle to each other so that the groove is at the broadest at the surface of the plate-like part of the mother plate. The groove can be created for instance by machining into the mother plate. The groove can also be created by attaching a metal profile to the mother plate so that the metal profile is one of the walls of the groove and the mother plate itself is the other one.
In a further embodiment a groove is created into the mother plate and this groove is filled in with material which has a poor conductivity. This groove is made so narrow that the metal deposit can grow over the area where the filling material is effecting, but it is not possible for the metal deposit to grow along the surface of the fill material. Thus the metal deposit grows over the surface of the filling material slower than on the surface of the mother plate and the metal deposit is thinner and, therefore, easier to be bent when the metal deposit is under the releasing process.
The growth affecting means creates on the mother plate an irregularity in the growth of the metal deposit which irregularity is advantageously used as a hinged member when the metal deposit created in the electrorefining or electrowinning process on the mother plate is removed from the mother plate with the separating device. When hinging the tilting angle of the metal deposit in relation to the mother plate of the cathode is advantageously between 60 to 150 degrees, preferably essentially 90 degrees. The metal deposit is for instance hinged on the growth affecting means from the surface of the mother plate up to an essentially right-angled position to the mother plate. The metal deposit can also be hinged on the growth affecting means by bringing the metal deposit in an up and down motion.
In the preferred embodiment of the invention the metal deposits from both sides of the cathode are simultaneously treated. However, it is also possible to treat the metal deposits separately. The cathode to be treated is supported in the essentially vertical position. The metal deposits on both sides of the cathode to be treated are first partly released starting from the edge where the hanger bar is installed. These partly released metal deposits are then tilted until the partly released metal deposits have a contact with the supporting members or the gripping member of the device. In this supporting position the metal deposits are gripped with at least one gripping member of the device and these gripping members are used to tilt the metal deposits so that the metal deposits are advantageously finally in an essentially horizontal position. When tilting the metal deposits to the essentially horizontal position the metal deposits are in at least partial contact with the mother plate of the cathode. During this tilting stage the growth affecting means of the mother plate is used as a hinged member so that the metal deposits are tilted around the area where the growth is affected by this growth affecting means.
In order to produce two separate pieces from one metal deposit in one embodiment of the invention, the essentially horizontal metal deposit with the gripping members is moved to the separation position and is broken along the growth affected area by pulling its ends into opposite directions by the gripping members. When the separation is completed, the gripping members release the metal deposits and the gripping members are returned for the treatment of metal deposits of a new cathode. The separation of the metal deposit into two separate parts can also be performed so that the breaking is done after the metal deposit has been tilted into a separation position and has released by the gripping members in a separate breaking station. The breaking is thus performed by pulling the ends of the metal deposit into opposite directions or by some other means of separation.
In one embodiment of the invention the metal deposits are completely separated from the mother plate by moving the gripping members in up and down motion in the tilting stage of the metal deposit so that the growth affecting means is used as a hinged member. During this up and down motion the metal deposit is completely separated from the mother plate around the growth affecting means.
In the separating device of the invention the cathode to be treated is supported in an essentially vertical position and the cathode maintains its position essentially during the whole time when the metal deposits are removed. The gripping members which are used for tilting the metal deposits to the essentially horizontal position, are moved along a guide member. The guide member installed on a frame member is pivotable connected to a frame member of the device. In one embodiment the separating member which finally separates the metal deposit from the mother plate, is advantageously installed on the same frame member as the guide member of the gripping members. It is also possible to install the guide member and the separating member so that they have different frame members of their own. The guide member is advantageously so arched that the center of the arc is co-axial with the line connecting the two sides of the metal deposit so that the metal deposits are tilted around the area where the growth is affected. In the essentially position of the metal deposit, the separating device provides a movement of the gripping members opposite directions causing the metal deposit to break along the area where the growth is affected, producing two separate pieces.
In still one embodiment the mother plate of the cathode can be lifted away from the at least partly released metal deposits prior to or during the up and down motion. The Ifting of the mother plate will make more effective the up and down motion of the metal deposits. In that case, it is preferred that the mother plate is supported by the hanger bar during the release of the metal deposits.
For the operation of the device of the invention, the desired movements of the members to be moved in different steps of the operation are created by regulating units which are operated pneumatically, hydraulically or electrically.